Hello, I don’t if there are Mac users suffering same problem with me. Once I installed OS X 10.8 Mountain lion on my iMac machine, my computer starting to run slow. Since downloading its been getting slower and slower, if I play a movie it freezes every 20 seconds, its just slow and laggy…any help? Does Mountain Lion really drag down a Mac’s performance? What should i do to speed it up?

This is nothing at all about “slow”. It is not about “laggy”. It is about “hang”. After an upgrade, I run Disk Utility, select the OS X partition, and verify/repair disk permissions. It doesn’t hurt to verify disk either. Try:

Restart while holding the command R keys for 45 seconds.

Choose “Disk Utility”.

Select the “Macintosh HD” and select the “First Aid” tab.

Click “Repair Disk”.

If it shows any problems, repair again.

If no problems at all were found, quit Disk Utility and restart.

Meanwhile, OS X Mountain Lion needs more free space to run it smoothly. Increase RAM or hard disk space. You can also use a Mac clean software available in market to get your iMac fresh and junk-free.

Note: every new OS should be more refined, feature-rich and responsive than the last, but it’s not always so rosy especially for people with older Macs or for people whose systems can’t quite cut the mustard in terms of specifications and performance. This article just lists just some of the reasons why Mountain Lion might runs slower than you’d like, and in a follow up article describe several ways how you can optimise your iMac machine to keep it running in tip-top condition.